The fuel cell has been proposed as a clean, efficient, and environmentally responsible power source for various applications. A plurality of fuel cells may be arranged to form a fuel cell stack capable of powering an electric vehicle. One example of the fuel cell is a Proton Exchange Membrane (PEM) fuel cell. In the PEM fuel cell, hydrogen is supplied as a fuel to an anode and oxygen is supplied as an oxidant to a cathode. A common technique for storing hydrogen is in a lightweight, high pressure vessel resistant to puncture. High pressure vessels containing the compressed hydrogen gas must have a desired mechanical stability and integrity that militates against an uncontrolled release of the compressed gas from the pressure vessel due to the internal pressure. It is also typically desirable to make the pressure vessels on vehicles lightweight so as not to significantly affect the weight requirements of the vehicle.
Known high pressure vessels include at least one thermally activated safety valve or pressure relief device (TPRD). The TPRD is located at a boss or an end of the high pressure vessel that houses various valves, pressure regulators, piping connectors, excess flow limiters, etc. for allowing the pressure vessel to be filled with the compressed hydrogen gas. The TPRD may also be located at another opening in the pressure vessel, though the TPRD generally is disposed at one or both ends of the pressure vessel. The TPRD is useful when the pressure vessel is exposed to high temperatures. More than one TPRD may be used where high temperatures might occur at a localized area apart from the location of the single TPRD. One known TPRD includes an elongated, fragile bulb coupled to an ignitable cord, which transfers heat to the TPRD from remote areas of the vessel. When heated to a predetermined temperature, the bulb breaks, thereby opening a venting aperture and actuating the TPRD. However, heat transfer to the TPRD by the ignitable cord is not suitable in certain applications and occasionally unpredictable. Further, the elongated bulb requires a large package size, as well as includes a significant volume of temperature sensitive material to be heated for actuation of the TPRD. Additionally, such a device may only be operated once. Following such operation, the TPRD is destroyed and must be replaced.
Another known TPRD is resettable. However, the trigger mechanism must be replaced, reset and tested after operation.
Another known TPRD has a thermally actuated trigger mechanism that interferes with a movement of a valve closure element. The trigger mechanism is formed of a shape memory alloy that expands when heated to a set temperature, eliminating the interference with the closure element and actuating the pressure relief device. This one-way shape memory trigger mechanism is expensive and involves several moving parts.
There is a continuing need for a TPRD that can be installed in a high pressure vessel for use with a fuel cell stack. Desirably, the TPRD includes a trigger mechanism that minimizes manufacturing cost.